Jensen’s alpha is a measure of a security’s excess return with respect to the expected return
given by the Capital Asset Pricing Model. Investors are looking for assets or portfolios with
positives alphas, as it signals positive abnormal return. An asset with a positive alpha has a
higher return than the risk adjusted return estimated by the CAPM. Computations of Jensen’s
alpha are based on realized returns. For a stock or portfolio i, we thus have: